In recent years, along with demands for smaller electronic equipment having advanced performance, a wiring board for use with electronic equipment has been demanded so as to allow for high-density mounting of electronic components and miniaturization. To achieve such demands, electronic components in a thin film form are incorporated in a wiring board for realizing high-density mounting, or three-dimensional mounting technology has been developed so that existing electronic components of semiconductors and capacitors can be built therein (see JP H06(1994)-32378 B2, for example).
One proposed example is a component built-in module, in which active components such as semiconductors and passive components such as capacitors are embedded in a composite sheet including inorganic filler and thermosetting resin.
Since this component built-in module contains a large amount of fine particles of inorganic filler, it has an excellent heat-radiation property and a low dielectric constant while allowing electronic components to be embedded therein easily. Thereby, the component built-in module allows its wiring to be shortened while having a shielding effect and so has a high noise immunity. Therefore such a component built-in module is effective as a wiring board operating at high frequencies, in which components are three-dimensionally mounted with high density.
As means for establishing continuity between upper and lower wiring patterns in the above component built-in module, a via hole may be formed in a composite sheet and this via hole may be filled with a conductive resin paste. Such a method for manufacturing a component built-in module is proposed in JP H11(1999)-220262 A, for example.
The following describes an example of a specific method for manufacturing a component built-in module, with reference to FIGS. 20 to 22. Firstly, as shown in FIG. 20A, protective films 1002a and 1002b are attached to both faces of an uncured composite sheet 1001 so as to form a sheet member 1003 of about 100 μm in thickness.
Then, as shown in FIG. 20B, a cavity 1004 corresponding to the shape of an electronic component 1301 (see FIG. 22A) to be built therein is formed in the sheet member 1003 by laser processing or punching. Next, as shown in FIG. 20C, the protective film 1002b on one side is peeled off, and a new protective film 1002c is attached thereto instead so as to cover the opening of the cavity 1004.
Then, as shown in FIG. 20D, a via hole 1005 is formed by laser processing or punching so as to penetrate through the sheet member 1003. Subsequently, as shown in FIG. 20E, the via hole 1005 is filled with a conductive resin paste 1006 by printing or the like. Then, as shown in FIG. 20F, the protective films 1002a and 1002c are peeled off so as to form a sheet member 1100.
On the other hand, as shown in FIGS. 21A to D, a sheet member 1200 is prepared by the process similar to the above for the sheet member 1100 except that no cavities are formed. The sheet member 1200 functions so as to prevent the interference between the built-in electronic component 1301 (see FIG. 22A) and a second wiring board 1400 (see FIG. 22A).
Then, as shown in FIG. 22A, the two sheet members 1100, the sheet member 1200, a first wiring board 1300 including a first wiring pattern 1302 and an electronic component 1301 mounted on the first wiring pattern 1302 and a second wiring board 1400 including a second wiring pattern 1401 are aligned with each other and stacked, followed by hot pressing, whereby the first wiring pattern 1302 and the second wiring pattern 1401 are connected electrically through via conductors 1501, 1502 and 1503 (see FIG. 22B for all) made of the conductive resin paste 1006. In this way, the component built-in module 1500 as shown in FIG. 22B can be manufactured.
According to the above-stated conventional manufacturing method, however, since at least two sheet members are stacked, misalignment might occur during stacking of the respective sheet members. If misalignment occurs among the respective sheet members during stacking, misalignment may occur as shown in FIG. 22B between a side face 1501a of the via conductor 1501 and a side face 1502a of the via conductor 1502 and between the side face 1502a of the via conductor 1502 and a side face 1503a of the via conductor 1503, and such misalignment may lead to the degradation in reliability for electrical connection.